Werb Z, Cohn Z A
J Exp Med. 1971 Dec 1;134(6):1570-90. doi: 10.1084/jem.134.6.1570.
Macrophage membrane cholesterol is present in two subcellular cholesterol pools, a rapidly exchanging compartment comprising about two-thirds of the total cholesterol, and a slowly exchanging compartment comprising one-third of the total. The morphological identification of the kinetically distinguishable pools proceeded by alteration of each compartment. Trypsin treatment markedly decreased the rate of cholesterol exchange without removing cholesterol from the membrane. Recovery of normal exchange rates took more than 7 hr and required protein synthesis. This suggested that a plasma membrane receptor is involved in positioning of lipoproteins for exchange, and is consistent with the plasma membrane localization of the rapidly exchanging compartment. Extensive pinocytosis by nondegradable dextran, dextran sulfate, or sucrose resulted in the accumulation of many secondary lysosomes, thus increasing the relative proportion of intracellular membranes. The measurable granule membrane area, cholesterol content, phospholipid content, and the relative size of the slowly exchanging cholesterol compartment all increased. The amount of intracellular membrane altered by extensive phagocytosis of latex particles also increased the size of the slowly exchanging cholesterol compartment. This suggested that the slowly exchanging pool of cholesterol represented the intracellular membranes primarily of lysosomal origin. Rabbit alveolar macrophages and thioglycollate-stimulated peritoneal macrophages contain many secondary lysosomes as a result of multiple bouts of in vivo phagocytosis and pinocytosis. In both of these cells the fast and slow pools are equal in size. The increased cholesterol content was attributable to the increase in the relative size of the slowly exchanging compartment. L-cells and melanoma cells also exchange their cholesterol with that of serum lipoproteins. Both cells contain few cholesterol-rich intracellular membranes, and had lower cellular cholesterol contents. In these cells the slowly exchanging pool was a minor contribution to cell cholesterol. Studies with these cells provided further evidence for the lysosomal membrane and plasma membrane localization of the slowly and rapidly exchanging cholesterol compartments.
巨噬细胞膜胆固醇存在于两个亚细胞胆固醇池中，一个快速交换区室约占总胆固醇的三分之二，一个缓慢交换区室占总胆固醇的三分之一。通过改变每个区室来对动力学上可区分的池进行形态学鉴定。胰蛋白酶处理显著降低了胆固醇交换速率，但并未从膜上除去胆固醇。正常交换速率的恢复需要超过7小时，且需要蛋白质合成。这表明质膜受体参与脂蛋白交换的定位，这与快速交换区室的质膜定位一致。不可降解的葡聚糖、硫酸葡聚糖或蔗糖的广泛胞饮作用导致许多次级溶酶体的积累，从而增加了细胞内膜的相对比例。可测量的颗粒膜面积、胆固醇含量、磷脂含量以及缓慢交换胆固醇区室的相对大小均增加。乳胶颗粒的广泛吞噬作用改变的细胞内膜量也增加了缓慢交换胆固醇区室的大小。这表明缓慢交换的胆固醇池主要代表溶酶体来源的细胞内膜。由于多次体内吞噬作用和胞饮作用，兔肺泡巨噬细胞和巯基乙酸刺激的腹腔巨噬细胞含有许多次级溶酶体。在这两种细胞中，快速和缓慢池的大小相等。胆固醇含量的增加归因于缓慢交换区室相对大小的增加。L细胞和黑色素瘤细胞也与血清脂蛋白交换它们的胆固醇。这两种细胞含有的富含胆固醇的细胞内膜很少，细胞胆固醇含量较低。在这些细胞中，缓慢交换池对细胞胆固醇的贡献较小。对这些细胞的研究为缓慢和快速交换胆固醇区室的溶酶体膜和质膜定位提供了进一步的证据。
